Cylindrical-parabolic solar collector plants are found within the different types of thermal solar plants. In these types of plants the thermal fluid traverses a straight pipe located in the actual focus of an extruded parabola. This parabola, the longitudinal axis of which can be oriented in a north-south or east-west direction, is in turn able to rotate on a single axis to optimize the incident radiation in the opening area of the collector.
Normally the dimensions of a collector of this type are usually around 100-150 meters in state-of-the-art collectors. These collectors, which move by means of a hydraulic mechanism, are formed in turn from several segments the length of which is about 12 meters.
Several methods for manufacturing the arms in the state of the art can be pointed out:
1. Arms Made Based on Welded Tubes:
Until now, the arms on which the mirrors are supported have been made from tubes welded to one another forming a small lattice. However this manufacturing method, providing a light and strong structure in the end, creates two fundamental drawbacks:                The manual labor associated to the cutting and welding of the tubes makes the end product considerably more expensive.        The precision finally obtained at the support points of the mirrors is not enough to directly support the mirrors. To that end it is necessary to use intermediate metal parts secured to the arm by means of guides which are finally adjusted to the desired position with the aid of a tool. This operation also has its impact on the final cost of the part.2. Other Alternatives:        
There are other alternatives for manufacturing arms for supporting the mirrors of cylindrical-parabolic collectors which can be emphasized:                Using fiber panels, sandwich panels or the like for generating very light and sufficiently resistant structures.        Using continuous structures which prevent using arms.        
The arms must also fulfill a series of characteristics:
1. Geometric Characteristics:
There are different arrangements of the bars for forming the arm depending on the loads for which the collector is sized, the position of the latter within the field and the measurements of the central case and of the original parabola forming the mirrors.
2. Physical Characteristics:
The following can be emphasized among the most important:                Weight of the arms: Between 10-14 kg/part.        Superficial treatment: Hot galvanizing.        Types of profiles used: normally a tubular profile having a thin wall (thickness 1-2 mm).        
The field collector, i.e. the set of all collectors collecting solar radiation in order to heat the oil, is a fundamental part in these types of stations. The collectors in which the mirrors are supported are made based on a metal structure, normally galvanized steel, and must fulfill the following requirements:                On one hand they must provide enough precision to position the mirrors such that they concentrate all the radiation on the geometric focus of the theoretical parabola.        On the other hand, and given the large dimensions which these stations usually have, the metal structure must be inexpensive, simple to manufacture and long-lasting.        
Throughout the history of these plants, different types of structures capable of satisfying, to a greater or lesser extent, these requirements have been developed.
Two types of support structures can fundamentally be distinguished between.                Collectors made based on what could be called “spatial structure”. In these collectors, the support structure forms a continuous whole extending through the entire rear part of the parabola. In these types of structures there is no distinction between central body and arms, all forming a monoblock assembly.        Collectors formed by a central body and arms supporting the mirrors. In these types of collectors the structure can be separated into two parts. On one hand is the central body fundamentally supporting the bending and torsion loads. This central body can be made based on a welded tube or by means of a framework of bars. Arms are fastened to this central body which are responsible for supporting the parabolic mirrors.        
The invention relates to these arms, to the central body and to the method for manufacturing said arms.